Freaking out! Gave my baby spoiled milk?

My husband took out 4 oz of my breastmilk to feed our son from the fridge, but my son only drank 1 oz of it at the time so we left it out and my breastfeeding lactation nurse told me it’s good for 4-6 hours so at 6 hours I fed him an oz, but stopped because I think it got close or it came to the time. Now I’m freaking out because I smell the milk and it smells nasty. Is he going to be okay? :(

I ended up giving him another bottle because I wasn’t trusting the one previous and he was so sleepy so he wasn’t drinking much but then spit a lot out so I’m hoping it was the spoiled milk. I smelt the spit up on his clothes and it smells like the bad milk